#include <iostream>
#include <math.h>
using namespace std;

int main() {
    double xa,ya,xb,yb;
    cin >> xa >> ya >> xb >> yb;

    double res;
    res = sqrt(pow((xa - xb), 2) + pow((ya - yb), 2));
    printf("%.3f", abs(res));
    return 0;
}